1. Field of the Invention
The present invention relates to supercharged internal combustion engines and more particularly to control systems for supercharged engines. More specifically, the present invention pertains to ignition timing control means for supercharged engines.
2. Description of Prior Art
Conventionally, it has been known to control superchargers for supercharged engines so that they are operated when the engine loads are above a predetermined value. For that purpose, supercharging compressors may be driven by electric motors which are energized when the engine loads are above the predetermined value. Alternatively, the supercharging compressors may be driven by engine crankshafts through clutches which are engaged when the engine loads are above the predetermined value. An example of the latter type system is disclosed in U.S. Pat. application Ser. No. 414,861, now U.S. Pat. No. 4,527,534, assigned to the same assignee as the present invention. A similar system is also disclosed in Japanese patent disclosure No. 58-44216, disclosed for public inspection on Mar. 15, 1983. The proposed systems, however, have problems in that there is a possibility of engine knocking being produced at a transient period just after the supercharger operation is started. More specifically, in a supercharged engine it is conventional to have the ignition timing retarded as compared with a non-supercharged engine, or to provide an inter-cooler in the intake passage in order to avoid the danger of knocking. In the engine having the supercharger operated only during engine operation wherein the engine load is greater than a predetermined value, the most practical way of avoiding the danger of knocking is to retard the ignition timing when the supercharger is being operated. For that purpose, the engine may be provided with a control system responsive to an increase in the intake air temperature, due to the compression by the supercharger, for retarding the ignition timing. However, with this control, there may be a possibility that the control of the ignition timing be delayed when the supercharger operation is started. Therefore, there still is a risk of knocking being produced in the transient period wherein the supercharger operation is just started.